Does Soy Milk Contain Isoflavones?

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Soy milk is a fluid produced by soaking, grinding and boiling soybeans. Soybeans, a member of the legume family of vegetables, serve as a valuable source of dietary protein and fiber, and also contain essential vitamins, minerals, fats and carbohydrates. Soybeans and the soy milk produced from them contain important plant substances known as isoflavones.


Scientists classify isoflavones as phytoestrogens, chemicals produced by a plant that can bind to estrogen receptors in the body. Soybeans serve as the most concentrated source of isoflavones in the human diet, according to the Linus Pauling Institute. The isoflavones in the plant bind to the sugar molecules in the soybeans and are released in the body during digestion. The isoflavones in soybeans and soy milk include genistein and daidzein, which differ only slightly in their chemical structure.

Role of Isoflavones

Because these compounds can bind to estrogen receptors, isoflavones may mimic the responses of the hormone estrogen. This can help prevent conditions like osteoporosis that occur because of low estrogen levels. When isoflavones bind to estrogen receptors, they also block estrogen from binding, reducing the effects of estrogen. This role can help reduce estrogen-dependent cancers like breast, uterine or prostate cancer.

Soy Milk Isoflavone Content

The process manufacturers use to extract the soy protein during the production of a soy food impacts that amount of isoflavones remaining in the food. Proteins extracted using an ethanol-wash process lose most of the isoflavone content, while those isolated using a water-wash process retain the isoflavones. Most commercially produced soy milk contains isoflavones, but the amount may vary by brand and even in different lots of the same brand. In general, a one-cup serving of soy milk contains 12 mg of diadzein and 17 mg of genistein, according to the Linus Pauling Institute.

Other Advantages of Soy Milk

Soy milk does not contain lactose, the specific type of sugar molecule found in cow's and other mammal's milk. This provides an advantage for the 30 to 50 million American adults that suffer from lactose intolerance, a condition that occurs when the body fails to break down lactose, according to the U.S. Department of Health and Human Services. For these people, soy milk serves as an alternative source of calcium. In addition, soybeans are the only common plant source of complete protein, meaning it provides all of the essential amino acids. Soy milk provides an amount of protein similar to cow's milk.